3. The number of houses on a block in San Roque is distributed as follows: X 4 5 7 8 12 P(X=x) 0.13 0.32 0.35 0.09 0.11 A block in San Roque is selected. a) What is the probability it does not have 6 houses? b) What is the probability that it has between 4 and 10 houses? c) What is the mean number of houses on a block in San Roque? d) Calculate the variance